1. Field of the Invention
This invention relates generally to work stations or work holders used in indexing semiconductor lead frames through an automatic wire bonder and, more specifically, to a precisor plate employed in such a work holder or work station adapted to be quickly readjustable to accommodate differently configured lead frames.
2. State of the Art
There are a limited number of companies in the semiconductor industry that manufacture automatic wire bonders used to form wire bonds on semiconductor devices. A leading manufacturer of such wire bonding machines is Kulicke and Soffa Industries, Inc. of Willow Grove, Pa., manufacturer of a work holder designated as model number 2810. These automatic wire bonders typically employ dedicated work holders which are adapted to receive a specifically configured lead frame. The work holders are coupled to or connected to at least three mechanical drives, one for advancing the lead frame, one for positioning the lead frame on the bonding station and one or more drives for clamping the lead frame in the station. Heretofore, changing the work holder required skilled technicians to disassemble and reassemble or partially rebuild the work holder to accommodate each differently configured lead frame and ensure that the new, differently configured lead frames will be precisely aligned with respect to the wire bonder. Such a reconfiguration process typically takes an hour or more with current work holders.
A typical work holder for a Kulicke and Soffa wire bonding machine includes a box-like frame attached to the machine through which lead frames are indexed, the box-like frame forming part of the work station at which lead frames are wire bonded. In addition, a precisor plate is attached to a vertical slider, the slider vertically moving the precisor plate beneath the lead frame. The precisor plate in conjunction with a heat block, typically rectangular in shape, supports the lead frame in the work holder and keeps the lead frame from moving during the wire bonding operation.
An attempt to provide a modular work station or work holder which is easily removed from and replaced in an automatic wire bonder is disclosed in U.S. Pat. No. 4,765,531 ('531 patent ) assigned to Kulicke and Soffa Industries, Inc., the manufacturer of the aforementioned model 2810 wire bonder. While the '531 patent is generally described. with respect to Kulicke and Soffa automatic wire bonder models 1481 and 1482, many of the components and their configurations are similar to the components of the model 2810 wire bonder. In the '531 patent, the problem of precisely aligning the precisor plate and heat block relative to the rest of the work holder is addressed by immobilizing the entire work station while various pins and bolts align and secure these components together and to the wire bonding machine. While the quick change work station described in the '531 patent may have been an improvement over the work holder stations of its time, the '531 patent work holder requires separate alignment of both the precisor plate and the heat block.
The work holder that is provided by Kulicke and Soffa with the 2810 model is as difficult, if not more, to align than the work holder described in the '531 patent. In addition to not providing a work station that can be quickly realigned, the precisor plate provided with the 2810 model wire bonder has moveable pins that must themselves be properly aligned to precisely engage tooling holes in the lead frame. In addition, the heat block must be separately aligned, and the precisor plate itself requires planarity adjustment, both right-to-left and front-to-back.
When a wire bonder as herein described is out of service, production on that machine is lost, resulting in a decrease in manufacturing efficiency. Accordingly, in order to avoid down time for realignment of the work holder, such automatic wire bonders are kept on line as long as possible, wire bonding similarly configured lead frames. In order to accommodate low production items, where only a few parts must be wire bonded, intermittent batch production, where the configuration of the wire bonder is frequently changed, or long production runs, where realignment of the precisor plate must be periodically performed, it would be desirable to provide a quick change precisor plate that can be simply and quickly adjusted.